Molecular markers for detection of resistance to chemotherapy

Objectives: The scope of this thesis was to select new biomarkers for the response to standard chemotherapies and new targeted therapies in ovarian cancer. Furthermore the utility of new platforms for the routine testing of biomarkers on RNA and DNA level was evaluated. Such markers are especially interesting for ovarian cancer as after initial good response to chemotherapy most tumors acquire multiple drug resistance (MDR). Material and Methods: Mutational status of KRAS was determined in fresh frozen and formalin fixed paraffin embedded (FFPE) ovarian tissue samples. The experiments were conducted on two different platforms, Gastoxin, a micro array system, and a reverse hybridisation strip assay. Gene expression of nine ATP-binding cassette (ABC) transporters were analysed in recurrent ovarian cancer samples and benign tissue with real-time Pcr. Transporters exhibiting a significant overexpression in recurrent disease were further evaluated in primary cancer tissue. Furthermore real-time Pcr results were validated with two novel platforms. Results: In 15% of ovarian carcinoma samples KRAS was mutated. Mutation rates in fresh and FFPE tissue were approximately the same which leads to the conclusion that both assays are able to process these types of tissue. Four of the ABC transporters were significantly higher expressed in recurrent cancer tissue. Primary lesions compared to benign tissue showed no mentionable differences in gene expression. Therefore the examined transporters are not feasible as prognostic markers but some seem to play a role in MDR of ovarian cancer. Regarding the two tested platforms, the Quantitating 2.0 Reagent System was found to be an adequate alternative to real-time Pcr. For the Approve-B platform the first optimization experiments were promising, further development is currently ongoing. Conclusion: Mutation of KRAS is no prognostic marker for patients under standard therapy, but in the light of the new anti-EGF R therapies, which are being tested in ovarian cancer, KRAS mutational status could become an interesting predictive marker in the near future. Although the examined ABC transporters are of no prognostic value in primary tumors, they seem to be one piece in the MDR puzzle of ovarian cancer and could eventually become therapeutic targets. The tested technological platforms should be further evaluated for routine use, since first experiments were throughout promising. (author)